HP Fortran Programmer's Guide (September 2007)

Writing HP-UX applications
Using HP-UX file I/O
Chapter 7 171
Establishing a connection to a file
HP-UX I/O system calls require an HP-UX file descriptor, which establishes a connection to
the file being accessed. A file descriptor is an integer whose function is similar to a Fortran
logical unit number. For example, the following open system call (called from a C-language
program) opens a file named DATA.DAT for reading and writing, and returns the value of an
HP-UX file descriptor:
#include <fcntl.h> /* definition of O_RDWR contained here */
...
fildes = open("DATA.DAT", O_RDWR)
Obtaining an HP-UX file descriptor
The Fortran intrinsic FNUM returns the HP-UX file descriptor for a given logical unit. See the
program in“File handling” on page 193 for an example of how to call the FNUM intrinsic. For
information about FNUM, see the HP Fortran Programmer's Reference.